Finding rental car discounts is somewhat of an art form. You have to be patient, look often, be prepared to¬†make changes¬†at the last minute and be organized enough to find the best deal. Rental car companies all do "Last Minute Specials" that are USUALLY the best deal, but from time to time you can find better deals through military discounts or through your bank. Some of the best discounts available for rental cars are available through USAA.
Once again, this is going to take research and patience on your part but will save you hundreds of dollars in the end.
Here are direct links to the military discounts of each of the major companies:
Enterprise, Avis and Budget use a third party to administer their military discounts and that company requires an annual membership fee to use their services. I NEVER recommend using anyone that charges you for access to YOUR discounts. These discounts are rightfully yours and you shouldn't have to pay someone to tell you about them.
Advantage and Fox are discount rental agencies in certain US cities and offer rates MUCH LOWER than the others. These discounts should be used with caution. I've personally used both companies and had no issue other than the cars being a bit older and less cared for (more stains, etc). I made sure to note every scratch and every issue BEFORE leaving the airport and had no trouble returning it when it was time. Be mindful and proactive and there are some great deals to be had.
If we can ever be of help or offer any advice, you can contact us anytime.